1. Field of the Invention
This invention is to some extent related to the inventions described in application Ser. No. 590,677, and in application Ser. No. 591,342, both of which were filed on Mar. 19, 1984.
The present invention relates to a module for a relatively large semiconductor chip which physically supports the chip and provides for heat dissipation and electrical connection to other elements in the system.
2. Description of the Prior Art
Semiconductor die or "chips" are normally formed in multiples in a silicon wafer, on the order of 5 inches in diameter. The wafer is then cut into individual chips, usually no larger than about 50 square millimeters, which contain a large number of electronic circuit elements. Logic chips which perform arithmetic computation functions, for example the function of addition, are now in production which have more than 40,000 transistors and other circuit elements in a 50 square millimeter area.
One limitation on the size of the chip has been the fact that electrical connections must be made between the various circuits on the chip and other circuits in the system. Typically, chips are rectangular with contacts along their two long edges, or square with contacts along all four sides, to which the necessary external electrical connections are made. As the size of the chip increases, the number of circuits which can be located on the chip increases much more rapidly than the number of contacts available on its periphery. Attempts have been made to provide a two dimensional array of contacts on one face of the chip, but the difficulty of making pin-point soldered connections between the flat surface of the chip and the flat substrate is itself a limitation on the size of the chip. The number of logic circuits which can be accommodated on a single chip is thus limited by the necessity of connecting the circuits to other system elements, and the chips themselves have been quite small.
A large number of relatively small chips are necessary to construct a computer of significant capacity. Each chip consumes a large amount of power, and accordingly generates a large amount of heat which must be dissipated to prevent malfunctions in the system. Present computer design concepts require that the chips be sufficiently spaced from one another so that convective cooling is sufficient to prevent overheating, which creates an unfortunate design constraint on the system. In modern high speed computers, the transmission time between elements in the system, typically the numerous chips used for logic and memory, is a significant limitation on system speed. At the present time, high speed computer design involves a trade-off between appropriate spacing of the chips to avoid overheating, and locating them sufficiently close together to provide short transmission paths between them so that system speed is not unacceptably degraded.
Recent attempts have been made to minimize the spacing between the chips by using water cooling, as typified by the chip mounting system utilized in the IBM 3081 computer, described in the June 1983 edition of Scientific American, pages 86-96. In this design, a large number of chips are mounted close together in a planar array on a multilayer ceramic substrate. Chips are used which have a contact array on one face; the multiple contacts of the array are soldered directly to corresponding contacts on the substrate. A "hat" overlies the numerous chips, and contains a number of heat conductive pistons which are spring-biased against the respective chips. A cold plate with interior water channels overlies the hat for heat dissipation. The IBM device thus decreases the required spacing between the chips by locating them closer together on a single substrate, and dissipating heat by the use of water cooling (with an intervening heat conducting "hat"), but does not alter the basic requirement of the prior art for large numbers of relatively small chips.